This invention is concerned with a thermometer instrument for use in sensing temperature changes in a fluid cooled electrical transformer and causing a signal corresponding to the change to be transmitted to an external indicator.
It has been found that when a temperature change in an electrical transformer exceeds a certain value for any appreciable period of time, the life of the transformer decreases rapidly. The indicator which reflects the temperature change may be informative to an attendant to take appropriate protective steps to control the operation of the transformer; or it may include automatically operable signal responsive control devices to this end.
It has been found that the hottest spot develops in the winding of the transformer. Accordingly, the thermometer should be associated with the winding for greater accuracy and rapidity in sensing any developing temperature changes that may prove harmful to the transformer if unduly continued.
However, problems are presented to the association of a thermometer with a transformer winding. The design of high voltage transformers is such that it is impractical to utilize in the winding any type of temperature sensing means having a metallic component. The introduction of a metallic element to the winding will result in distortion of the electrical flux path with a resultant reduction in transformer efficiency. These transformers presently operate above ground at very high potential so that no conductive material, such as a thermo-couple or other sensing device, can be utilized in the winding or connected to the transformer case. Connections between the sensing device and the case of the transformer must also be of a dielectric material to prevent a fault to ground in the transformer winding.
The general objective of the present invention is to provide a thermometer for sensing temperature changes in a fluid cooled electrical transformer which may be inserted in the winding of the transformer without developing the foregoing problems.
A further objective of the present invention is to provide a thermometer which may be inserted in the winding of a fluid cooled electrical transformer and which may be connected through the case of the transformer to suitable signal indicating means.